How to Spray Water Based Finishes
General Finishes water based products can be sprayed through compressed air, HVLP, airless or C.A.S. units. Surface Preparation: All surfaces should be clean and free from dirt and oil and sanded as per instructions above. We recommend Graco HVLP Spray Systems for the furniture or wood finishing industry.
Spray Application of General Finishes Water Based Finishes Using HVLP Spray Equipment
- Water Based top coats are ready to spray from the container. If necessary in hot or dry climates, reduce 10 to 20% with water or General Finishes Extender to extend the open time.
- Pre-Sealing: Softwoods such as Pine and Aspen absorb stain at an uneven rate and may respond better to staining if the wood has been pre-sealed. Natural stain can be applied to raw wood to condition the surface for uniform penetration of the stain. Pre-sealing will cause the final stain to be lighter. Always test your colour on a hidden part of the furniture! Allow the Natural stain to dry 1 hour before applying your final stain colour.
- If you are using a sprayer that has been used for oil based or lacquers, clean the unit thoroughly and rinse with warm water before using. Apply a thin coat first that will dry and harden faster. Sand this first coat down to a smooth base on which to build your finish coats. With water-based finishes, it is better to spray 2 thin coats rather than 1 heavy coat.
- Recommended Spray Tips for Wood Stains and Top Coats. Fluid tip sizes for HVLP should be as follows:
- Dye Stains 1.1mm
- Wood Stains 1.1mm to 1.3mm
- Top Coats 1.1mm to 1.3mm
- Milk Paint 1.8mm
Contact your supplier to verify proper tip sizes for your specific equipment.
- Always strain material through a medium to fine mesh filter before spraying.
- Spray medium wet films at 3-5 wet ml thickness.
- Reduction: If spraying the product as a stain in order to allow the grain to show through, reduce 10 to 20% with water or General Finishes Extender. If spraying as a paint, do not reduce. For example, you may wish to spray Rosewood stain on for a painted look. In this instance, do not reduce. It is generally not necessary to reduce Milk Paints. but they also may be reduced 10 to 20% with water or GF Extender.
- Practice makes perfect! If you have never sprayed finishes before, take a large piece of cardboard and practice your technique first. Spray water on the cardboard to learn how the gun works. Check your fluid settings and adjust the controls to get comfortable with the spray angles and to develop your technique.
- Keep your gun at a 90* angle, 15 - 20cm from the surface. On large flat areas, use wet, even patterns 15 - 20cm wide. Overlap each pass 25% to conceal lines.
- For narrow surfaces, reduce the fan pattern to 5 - 7cm to reduce overspray. Break your work into sections such as dresser top or drawer fronts. Spraying too large of an area can result in a textured grainy surface. A correctly sprayed finish should appear even and glossy. It is important to spray enough material to allow proper flow and levelling of the finish.
Trouble Shooting Guide for Spraying Water Based Finishes
- Rough, dry surface. This is called dry spray. You may have sprayed too lightly. Re-sand the finish with #320 paper and apply a heavier coat. Keep your gun at 15 - 20cm from the surface.
- Dimples in the finish. This is called orange peel, caused by spraying in temperatures that are too cool. Cooler temperatures will adversely affect how the finish will level and harden. Water-based finishes must be applied at temperatures above 18C. If it is cold enough to wear a sweater it is too cold to apply a water-based finish. The surface of the wood must also be warm. If you turn the heat on when you enter your shop in the morning, the air heats up quickly but your furniture will still be cold for some time. Check the surface to see if it is warm. Also, check the temperature of the finish. Warming cold finish by setting the can next to a heater or setting the container in some hot water for 5 minutes will improve the ease of application. Note: Larger dimples are called "fish-eyes" or "craters". Cool temperatures can cause these, but the more likely source is contamination of the finish with either wax or silicone
- Blush. Blush, the term for a cloudy, milky appearance in the finish, has two causes. The most common reason is an incompatible stain. For example, using a water-based top coat over a heavy oil-based stain. When the top coat is applied, the oil in the stain seeps up through the finish and reacts with the acrylic causing a chemical blush. To prevent this, use a quick-drying water-based stain. If you choose to use oil-based stain, seal the stain with a coat of shellac or lacquer sealer. This will provide a barrier between the oil and the acrylic. Proper drying time between the oil stain and finish coats is essential! The other cause for blushing is high humidity. Spraying water based finish in humidities of over 75% may cause blushing because moisture becomes trapped beneath the finish and cannot evaporate. You can prevent this condition by increasing air movement in the finishing area with a fan. All water needs to evaporate is sufficient air movement. You can also improve drying conditions by increasing the temperature in the drying area.
- The surface is not levelling out. In hot temperatures (30C +) the finish may dry too fast. Use General Finishes Extender to open (increase) the dry time. Finishes that dry too fast may not completely level out before all the water evaporates from the finish.
Note: High humidity can cause the finishes to take longer to dry but will not harm the final finish.